This section introduces aspects that may help facilitate a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
Vertical optical grating couplers are often used to diffract light largely vertically from a silicon photonic chip to free space so that the light may be collected at an end of a single mode optical fiber located above the grating coupler. Typically, to avoid back reflection into the waveguide, the fiber is tilted to have an off-normal angle, and the grating coupler is designed to have a correspondingly aligned off-normal radiation angle. The use of such off-normal tilt angles, however, presents difficulties with device packaging and requires two angular alignments. Efforts to improve the match between the off-normal radiated field and mode of the tilted single mode fiber by apodizing the grating elements can present fabrication challenges related to reproducibly matching the Gaussian mode of a single mode optical fiber. The optical coupling efficiency can be improved by placing a mirror above or below the grating coupler to reflect light into the fiber, but, there are challenges to construct a mirror that reflects light with an off-normal radiation angle to enable efficient coupling to the end of such a tilted single mode optical fiber.